This invention relates to a device, e.g., a display device, an electro-optical shutter for a printer or the like fort effecting electro-optical conversion by utilizing spontaneous polarization of a ferro-electric liquid crystal and its negative dielectric anisotropy.
Electro-optical conversion devices which utilize the spontaneous polarization of ferro-electric liquid crystal and its negative dielectric anisotropy have been known in the art to this date such as the device disclosed in Japanese Patent Laid-Open No. 176097/1985.
FIG. 2 of the accompanying drawings is a perspective view of a conventional ferro-electric liquid crystal cell (which will be hereinafter referred to as a "liquid crystal cell"). Reference numeral 1, 1 represents a pair of transparent glass substrates that are arranged to face each other. Reference numeral 2, 2 represents an alignment membrane which is oriented uniaxially and horizontally, and is disposed on an inner flat surface of the substrate 1. A rubbing film of polyimide, for example, is used as the alignment membrane. The rubbing direction of the pair of alignment membranes is substantially parallel. Reference numeral 3 represents a ferro-electric liquid crystal such as a chiral smectic liquid crystal (which will be hereinafter referred to as "SmC*". It has spontaneous polarization in a direction othogonal to the major axis of the liquid crystal molecule (hereinafter referred to as a "molecular axis"). Here, those liquid crystals which has negative dielectric anisotropy .DELTA..epsilon. above at least a predetermined frequency are particularly selected as the ferro-electric liquid crystal. That .DELTA..epsilon. is below 0 (.DELTA..epsilon.&lt;0) means that dielectric polarization occurs in a direction orthogonal to the molecular axis due to an external electric field having a predetermined frequency range. The molecules of SmC* 3 are sandwiched between the substrates 1 and 1, exhibit horizontal alignment by the influence of the alignment membranes 2 and 2 as shown in the drawing and form a layer. Reference numerals 4 and 5 represents a pair of electrodes which are arranged to face each other in order to clamp the SmC* 3 membrane between them and to apply a driving voltage.
FIG. 3 is a driving waveform diagram of a conventional liquid crystal cell. A first DC pulse having a positive polarity is applied between the electrodes 4 and 5. However, the electrode 4 is kept at .theta. ground potential. Then, the liquid crystal molecules are aligned in such a fashion that the spontaneous polarization 6 of each liquid crystal molecule is arranged to a position perpendicular to the electrode 4 (see FIG. 2). This is the first stable state 7, under which the molecular axis is inclined by +.theta. with respect to the normal 8 of the SmC* layer. Next, when an AC pulse is applied, dielectric polarization occurs in a direction perpendicular to the molecular long axis because the liquid crystal molecule has negative dielectric anisotropy, and the first stable state is maintained and fixed by dielectric torque. When a second DC pulse having a negative polarity is further applied between the electrodes 4 and 5, the liquid crystal molecule is responsive to this pulse and the spontaneous polarization 6 of each liquid crystal molecule is aligned in a state where it faces pependicularly the electrode 5. This is the second stable state 9, where the molecular axis is inclined by -.theta. relative to the normal 8 of the SmC* layer (see FIG. 2). Thereafter, when an AC pulse is applied, this second stable state is maintained. Namely, the first stable state is written by the positive DC pulse, the second stable state is written by the negative DC pulse and the stable state is maintained by the AC pulse.
Turning back again to FIG. 2, reference numeral 10, 10 represents a pair of polarizations whose polarization axes cross each other at right angles. They clamp the SmC* membrane 3 and optically discriminate between the liquid crystal domain under the first stable state and the liquid crystal domain under the second stable state by utilizing birefringence. For instance, the first stable state is discriminated as a light cut-off state (hereinafter referred to as "black") and the second stable state, as a light transmission state (hereinafter referred to as "white").
The prior art reference already described discloses that the electrode arangement of the liquid crystal cell is of a matrix structure type such as shown in FIG. 4 and the scanning electrode group 4 (hereinafter referred to as "segment") and the signal electrode group 5 (hereinafter referred to as "common") are arranged to face one another. However, this reference does not disclose a driving waveform and a drive circuit for actually effecting line sequential driving. It is not possible to effect matrix driving by the waveform shown in FIG. 3.